PRIOR ART It is known that one of the important problems one comes up against in the therapy of the pathologies of the central nervous system (CNS) consists in the possibility for drugs to pass through the hematoencephalic barrier. In fact several compounds are known which prove to be endowed with remarkable in vitro activity, and then potentially useful as drugs for the CNS which, however, do not show any pharmacological activity when they are administered in vivo owing to their inability to pass through the hematoencephalic barrier.

Several strategies have been proposed in order to improve the capacity for a drug to pass through the hematoencephalic barrier and among these ones the design of prodrugs certainly represents one of the most promising.

The design of prodrugs useful for this aim mainly provides for the conjugation of an active drug with a substance able to give to the conjugate such characteristics to allow it a greater penetration of the hematoencephalic barrier. Moreover for the success of the prodrug it is proper that the bond between the drug and said substance is such as to allow, once passed through the hematoencephalic barrier, the reconversion of the prodrug in the starting drug. Up to now the major part of the research efforts has been aimed towards prodrugs showing a lipophilia increase which seems to be a. critical parameter for the crossing of the

hematoencephalic barrier (Hansch C, Bjorkroth JP, Leo A Hydrophobicity and central nervous system agents: on the principle of minimal hydrophobicity in drug design. J Pharm Sci 1987 Sep; 76 (9): 663-87).

However such a strategy does not allow the tissue specific accumulation and the achievement of the effective optimal concentration and further it generates side effects on other organs and tissues.

According to another approach, starting from substances active on the CNS which as such have poor application in therapy owing to their incapacity to cross the hematoencephalic barrier, prodrugs with aminoacids or glucose have been prepared allowing the active substance to be carried inside the CNS by a simplified mechanism based on specific carriers, and to be subsequently released in such a way to bring its specific pharmacological action. (Bonina F. P., Arenare, L., Palagiano, F., Saija, A., Nava, F., Trombetta, D., De Capraris, P. Synthesis, stability and pharmacological evaluation of nipecotic acid prodrugs. J Pharm,. Sci., 88,561-567,1999).

The pharmacological application of these carriers is limited by some problems. In the specific case of the GLUTs a limit is represented by the hematic levels of glucose, which may affect the transport efficiency because the carrier is completely saturated in case of hyperglycemia (Battaglia G., La Russa M., Bruno V., Arenare L., Ippolito R., Copani A., Bonina F., Nicoletti F., Systematically administered D-glucose conjugates of 7-chlorokynurenic acid are centrally available and exert anticonvulsivant activity in rodents. Brain Research 860,149- 156,2000). Another limit is represented by the fact that such carrier did not show to be effective for some drugs as in the case of the nipecotic acid. (Bonina Fp.,

Arenare L., Palagiano F., Saija A., Nava F., Trombetta D, de Caprariis P., Synthesis, stability, and pharmacological evaluation of nipecotic acid prodrugs. J.

Pharm Sci 19999 May; 88 (5): 561-7).

SUMMARY The applicant surprinsingly found that compounds potentially active for the treatment of the CNS pathologies, unable to cross as such the hematoencephalic barrier, become able to cross the hematoencephalic barrier when they are transformed into prodrugs by conjugation with covalent bond with the ascorbic acid, directly or by a linker, in the 5 and/or 6 positions. Said covalent bond is split by enzymes present in the brain in such a way to restore the active compound in the initial form.

The prodrugs according to the present invention have the following general formula (I) or (II) wherein W is a linker having formula

Y is selected from OR, NHR and halogen, m is zero or 1, n is zero or a number from 1 to 10, and when m is zero, R is a hydrogen atom or an active substance having a carboxy group binding with ester bond to the OH group of the ascorbic acid in 5 and/or 6 position and when m is 1, R is a hydrogen atom or an active substance having a hydroxy, thiol or amino group binding to the carboxy group of W with ester, thioester or amide bond, in 5 and/or 6 position, provided that R can not be simultaneously a hydrogen atom in both the 5 and 6 positions.

The active substances to use for the preparation of the prodrugs according to the present invention are selected from the group consisting of antioxidants, not steroid anti-inflammatories, adenosinic agonists, antagonists competitive of the NMDA, AMPA and Kainico receptors, agonists and antagonists of the metabotropic receptors, GABA uptake inhibitors, antivirals, anti-tumours ed antiepileptics.

The present invention also includes a method for the preparation of said prodrugs and the pharmaceutical compositions containing them.

DETAILED DESCRIPTION OF THE INVENTION The characteristics and the advantages of the prodrugs derivatives of the ascorbic acid suitable to the passage of the hematoencephalic barrier according to the present invention, will be mostly illustrated during the following detailed description.

The prodrug having formula (I) as defined in the summary, wherein m is zero, is prepared according to the following synthetic scheme. wherein RX represents an active substance having a carboxyl group or a salt or an ester thereof or the corresponding acyl chloride, R3 and R4 represent

protective groups selected in the group consisting of benzyl, benzoyl, dimethylterbutylsilyl, trimethylsilyl or acetyl.

The protective groups, R3 and R4, are able to easily release the hydroxy groups.

Preferably as a protective group benzyl is used allowing an easy purification and then higher global yields.

More specifically the ascorbic acid or one of its derivatives protected in 2 and 3 position or a salt thereof is made to react with (4) which is a biologically active substance containing a carboxy group or a salt or ester thereof or the corresponding acid chloride to give the corresponding derivative of the ascorbic acid or a salt thereof. This reaction is carried out in the presence of a condensating agent such as dicyclohexylcarbodiimide or high concentration sulfuric acid. For example when the sulfuric acid is used as a condensating agent, the sulfuric acid and the ascorbic acid or the 2,3-dibenzylated or the 2-phosphate ascorbic acid and an active substance provided with a carboxy group or an ester or salt thereof are mixed and made to react. The reaction times range from 1 to 120 hours, preferably from 4 to 50 hours, and the temperature is generally between 5 and 80°C and preferably between 20 and 35°C. The amounts of reactants are preferably equimolar and the reactants have a moisture content less than 5% and preferably they are anhydrous. The solvents used for the reaction may be organic polar solvents, preferably dimethylformamide. In case the condensating agent is sulfuric acid this one may also be used as a solvent. As an alternative the halide of the corresponding carboxylic acid may be used. The purification may be carried out by traditional techniques such as extraction or column chromatography and subsequent crystallization. When the ascorbic acid is

used its extraction turns out to be difficult, therefore it may be advantageous, in order to increase the yields, to use the derivative of the 2,3-dibenzylated ascorbic acid which is easily extractable from the aqueous medium retaining the reaction impurities. Such an alternative however needs the subsequent release with hydrogen and catalysts or BC13 and subsequent purification, after filtration on celite and evaporation of the solvent by crystallization.

In the event that the use of a linker (spacer) is provided for, that is in the event that in the formula (I) m = 1, the reaction may be carried out as from the following synthetic scheme, analogous to the previous one, providing for the reaction of the ascorbic acid or one of its protected derivatives, with a compound (7) suitable to give the spacer (linker) group and the subsequent condensation with the alcohol, thiol or amino group of a RX1 active substance. The R3 and R4 groups are as defined above while RX1 represents a biologically active substance containing at least an alcohol, thiol or amino residue.

Said compound (7) suitable to give the linker is preferably the succinic acid or the tartaric acid.

The products having formula (II) can be prepared with minor changes of the above operations, well known in the art.

The prodrugs derivatives of the ascorbic acid of the present invention may be used in compositions for medical use in all those pathologies of the CNS (cerebral and myocardial ischemiae, neoplasiae, inflammation, bacterial and viral infections) where there are difficulties to vehiculate in a specific way the biologically active substances to the CNS.

Substances active on the CNS suitable to the preparation of the prodrugs according to the present invention preferably belong to the following pharmaceutical groups. a) Antioxidants. In the last years the involvement of the oxidative component in the acute and chronic neurodegeneration, and in the damage associated to the post-ischemic reperfusion has been extensively confirmed. A compound developed and patented by us, Fe-FI-21 or its analog Trolox, as water soluble derivatives of alpha-tocopherol is particularly useful.

n=O Trolox n=1 Fe-FI-21 b) Not steroid anti-inflammatories. An alternative approach to the treatment of the neurodegenerative pathologies is suggested by numerous experimental evidences showing an inverse correlation between the use of anti-inflammatory drugs and the incidence of the above cited pathologies. Among the anti- inflammatories the diclofenac, the meclofenamic acid, indomethacin, naproxen etc. may be cited. c) Adenosinic agonists. It is known that adenosine is able to regulate several functions at the CNS and cardiovascular level. The activation of the A1

adenosinic receptors showed a series of effects, among which a depression of the neuronal irritability. On the basis of these effects the A1 adenosinic receptors have been proposed as a target for the development of drugs against the disorders caused by ischemic states at the cerebral level. The N6 derivatives substitutes of the adenosine have been reported to be powerful A1 agonists, and in particular the N6-cyclopentyl-adenosine (CPA), which is at present considered a prototype of the A1 agonists. d) Receptor competitive antagonists. NMDA, AMPA, Kainico, for example 7- chlorokynurenic acid; D-2-amino-phosphonopentanoic acid etc.; e) Agonists and antagonists of the metabotropic receptors, for example 1- aminoindan-1,5 (RS) dicarboxylic acid etc. f) GABA uptake inhibitors. An alternative approach to the treatment of pathologies such as for example Parkinson, Huntington's chorea and epilepsy provide for a strengthening of the central GABAergic activity. Among the in vitro potentially very effective compounds, the nipecotic acid has been selected, which is one of the most powerful in vitro inhibitors of the neuronal and glial uptake of GABA. g) Antivirals. Zidovudine (AZT) is one of the most effective drugs for the treatment of AIDS, but it has a high toxicity which limits its use.

Active substances particularly suitable to the use for the preparation of the prodrugs according to the present invention are selected from the group consisting of 7-chloro-kynurenic acid, D-2-amino-5-phosphonopentanoic acid, 1-aminoindan- 1,5 (RS) dicarboxylic acid, meclofenamic acid, indomethacin, naproxen, valproic acid, nipecotic acid, trolox, AZT, acyclovir and CPA (N6-cyclopentil-adenosine).

The preferred prodrugs of the present invention are: the prodrug consisting of 7-chloro-kynurenic acid or nipecotic acid or trolox bound with ester bond to the ascorbic acid in position 6; the prodrug consisting of 7-chloro-kynurenic acid or nipecotic acid or trolox bound with ester bond to the ascorbic acid in position 5; the prodrug consisting of 7-chloro-kynurenic acid or nipecotic acid or trolox bound with ester bonds in the positions 5 and 6 of the ascorbic acid.

By the prodrugs according to the present invention a biological experimentation has been carried out which showed that they are able to easily cross the hematoencephalic barrier.

In particular a biological experimentation has been carried out in order to determine the effects of the 6-O-nipecotil-ascorbate in the prevention of the convulsions induced by pentylenetetrazole (PTZ).

For the experimentation Swiss albinic rats have been used having a body weight equal to 25-30 g. In any experimental session a maximum number of 15 animals has been i. p. injected with saline solution (control), nipecotic acid (0.75 mmol/kg), 6-O-nipecotil-ascorbate (0.75 mmol/kg) respectively.

25 minutes after said treatment, every rat has been subcutaneously injected with pentylenetetrazole (80 mg/kg) and they have been observed for the subsequent 30 minutes by an observer who did not know anything about the treatment.

In order to estimate the effects induced by the treatment with pentylenetetrazole latency (sec) at the appearance of generalized tonic convulsions and mortality have been measured.

Mortality has been defined as the percentage of animals dead within 60 minutes

from the injection with pentylenetetrazole.

The statistical analysis of the results has been carried out by the ANOVA method followed by the Newmann-Keuls test for multiple comparisons.

The following results have been obtained.

The rats treated with 6-O-nipecotil-ascorbate and with nipecotic acid did not show apparent abnormality in the general behaviour except for a light dejection which appeared 40 minutes after the injection only in the animals treated with 6-O- nipecotil-ascorbate.

The results relating to latency (seconds) of the appearance of the tonic convulsions induced by pentylenetetrazole (PTZ) are reported in Table 1 TABLE 1 PTZ 80 mg/kg s. c. Control 6-O-Nipecotil-ascorbate Nipecotic Acid (saline solution) (0.75 mmol/kg i. p.) (0.75 mmol/kg i. p.) 660 925 680 680 810 521 605 1440 436 640 725 712 521 711 665 621.2 922.2 602.8 27.95 134.95 53. 04 5 5 5 As one may notice from the table the injection of 6-O-nipecotil-ascorbate produced a significant increase of the latency of the appearance of tonic

convulsions induced by pentylenetetrazole, thus showing an effect on the CNS implying the passage through the hematoencephalic barrier.

The prodrugs according to the present invention may be prepared in conventional pharmaceutical forms such as tablets, capsules, liquid preparations or injections in mixture with pharmaceutically acceptable diluents or excipients. The dosage depends on the subject which must be treated, on the pathology at issue and by the administration route and it may range between 0.05 and 100 mg/kg of body weight, preferably between 0.5 and 25 mg/kg of body weight per day for oral administration and preferably between about 1 and 10 mg/kg of body weight for parenteral administration, preferably between 0.05 and 10 mg/kg of body weight when administered by injection.

The derivatives of the ascorbic acid described in the present invention are usable in pharmaceutical compositions as active components in amounts which may range between 0.01 and 100%.

Examples of compositions for oral administration include tablets, pills, granules, powders, capsules, syrups, emulsions, suspensions and preparations for nebulization. These compositions may be obtained by known methodologies using excipients such as lactose, starch, saccharose or magnesium stearate.

By parenteral administration a composition by injection, a suppository, a cataplasm, an ophthalmic solution or a preparation for external application may be prepared. The suppositories include the endorectal and vaginal ones. The preparations for external applications include ointments, agents for nasal administration and agents for oral administration.

For the external applications, the compositions of the present invention may be

prepared in a solid, semisolid or liquid solvent according to known methods. For example in the case of a solid composition, the compounds of the present invention are added in powder form to an excipient (for example glycol, mannitol, starch, cellulose) or to a firming agent (for example gum arabic, cellulose derivatives, acrylic polymers).

In the event of an injection, the composition may be prepared as oil or aqueos suspension. In the event of a semisolid composition an aqueous or oily gel or an iontment is preferred.

An agent to adjust the pH (for example carbonic acid, phosphoric acid, hydrochloric acid, sodium hydroxide) and an antiseptic (for example para-hydroxy benzoic esters, benzalkonium chloride) may be added. In order to obtain suppositories, the compositions of the present invention may be put into a solid, semisolid or liquid suppository having aqueous or oily nature according to known methodologies.

EXAMPLE 1 <BR> <BR> Piperidin-, 3-carboxylic-3-[2-(3X4-bis-benzyloxy-5-oXo-2, 5diidrofuran 2-il)-2- hydroxy-ethyl] 1-tert-butyl ester acid To a solution of N-BOC nipecotic acid (1 g, 4.36 mmol), DMAP (dimethylamino- pyridine) (42 mg, 0.165 mmol) and 2,3 di-O-benzyl ascorbic acid (1.55 g, 4.36 mmol) in anhydrous CH3CN (62 ml) at 0°C, a solution consisting of N, N'- Dicyclohexylcarbodiimmide (DCC) (525 mg, 2.85 mmol) in anhydrous CH3CN (9 ml) is slowly added.

The reaction mixture is stirred at room temperature for 3 hours, in inert argon atmosphere. After evaporation of the reaction solvent under vacuum, the product

has been dissolved in Et20, washed with an aqueous solution di 1 N HCI (20 ml), then Brine (20 ml), NaHCO3 (20 ml) and anhydrified with Na2SO4. The organic phase is evaporated to dryness, and the residual product purified by silica gel EtOAc/esane (2/8) chromatography to give 1.06 g of the desired conjugation product, as a light yellow oil (Yield 43%) 1H NMR (CDC13) : 8 1. 2 (m, 9H, Boc), 1.3-1.4 (m, 2H, C5-H), 1.8-2.1 (m, 2H, C4-H), 2.5 (m, 1H, C3-H), 2.7-3.6 (m, 2H, C6-H), 3.85-4.0 (m, 2H, C2-H) 4.05-4.48 (m, 3H, C6'-H, C5'-H); 4.8 (d, 1H, J=2 Hz, C4'-H); 5.2 (m, 4H, CH2-Ph); 7.25-7.4 (m, 10H, Ph).

Maldi MS: 590.7 Da (M + Na) +; 606.7 (M+K) + <BR> <BR> 3-carboxylic piperidin-2- (3, 4-bis-benzyloxy-5-oxo-2, 5-diidro-furan-2-il)-2- hydroxy-ethyl ester acid To a solution of the previously obtained conjugate (1.21 g, 2.1 mmol) in anhydrous CH2CI2 trifluoroacetic acid (3.8 ml) is slowly added, and the mixture is stirred at room temperature for 2 hours, in argon inert atmosphere. The reaction solvent is removed under vacuum, the residue is taken back with CH2CI2 (20 mi) and subsequently washed with a solution of saturated NaHCO3 (2 x 20 ml). The organic phase is anhydrified with Na2SO4 and evaporated to dryness. The residual product is purified by silica gel chromatography with CH2CI2/MeOH (9/1) to give 630 mg (63% of yield) of the desired product, as a yellow oil.

1H NMR (CC) CI3) : 8 1. 3-1.4 (m, 2H, C5-H), 1.8-2.1 (m, 2H, C4-H), 2.5 (m, 1H, C3- H), 2.7-3.6 (m, 2H, C6-H), 3.85-4.0 (m, 2H, C2-H) 4.05-4.48 (m, 3H, C6'-H, C5'- H); 4.8 (d, 1H, J=2 Hz, C4'-H), 5.2 (m, 4H, CH2-Ph); 7.25-7.4 (m, 10H, Ph).

Maldi MS: 469.0 Da (M+H) +; 490.7 (M+Na) +; 506. 6 (M+K) +

Piperidin-3-carboxylic-2- (3, 4-dihydroxy-5-oxo-2, 5-dihydro-furan-2-il)-2- hydroxy-ethyl ester acid To a solution of the previously obtained product (1 g, 2.14 mmol) in MeOH (50 ml), Pd/C 10% (200 mg) is added, and the mixture is kept under stirring for 5 hours, at room temperature, in argon inert atmosphere. The reaction mixture is filtered on celite, and the solvent is removed under vacuum. The residual product is purified by silica gel chromatography, with CH2CI2/MeOH (8/2) to give 510 mg of the final deprocteted product as a light yellow oil (Yield 83%).

1H NMR (DMSO-d6) : 5 1. 3-1.4 (m, 2H, C5-H), 1.7-2.0 (m, 2H, C4-H), 2.4 (m, 1H, C3-H), 2.5-3.5 (m, 2H, C6-H), 3.65-3.8 (m, 2H, C2-H), 4.05-4.48 (m, 3H, C6'-H, C5'-H); 4.6 (d, 1 H, J=2 Hz, C4'-H).

Maldi MS: 288.4 Da (M+H) +.